Popular Plasma - Massless - plasma tweeter

A previous reseller of the Ionovac in Germany, Otto Braun (1928-2020), created an updated plasma tweeter in 1978. His company Corona Acoustic developed the Corona types 314-514. Again a slight misnomer as this was a glow discharge plasma tweeter and not a corona discharge based speaker. It is similar to the Ionovac in that a plasma is created in a quartz tube which is horn loaded and driven by local circuitry at the rear. Their description of its operation differs from what may be found here for plasma tweeters as it doesn't include any thermal characteristics in the explanation, it is described more closely to an ion wind speaker. That doesn't quite fit the physics but we can agree to disagree as these devices are difficult to classify.

This plasma tweeter has had one of the longer lifespans of a massless speaker as the production of it was taken over in 1998 by Lansche Audio who still sells it. Acapella (formerly ATR) also have a current model, the Ion-TW-1, which was also originally designed by Otto Braun. That is now sold as part of their high end loudspeaker systems. None of these appear to have obtained patents or licensed their designs, which would make sense from the amount of prior art.

Around the same time, in 1978, the Hill Type-1 Plasma Speaker System from Plasmatronics Inc. was demonstrated in the US, patented in 1979. This well known commercial product, often known just as the Plasmatronic, was a full range speaker system using a unique plasma tweeter based on a DC bias system instead of RF and with several plasmas rather than being horn loaded. Notorius for its use of helium tanks in the speaker cabinet, the helium was gently flowed into the plasma tweeter chamber preventing it from creating any noxious gases. It seems that little attention was paid to this major negative issue of high voltage massless speakers until now. Without some measures taken all types of plasma/ion/corona loudspeakers react with the air to create ozone and NOx. These toxic gases are harmful, especially in closed rooms where concentrations can build to harmful levels. By replacing the air locally with an inert gas no reaction can take place so no toxic gases are produced.

The Hill Type-1 was reviewed well in articles from Popular Science (1979), International Audio Review (1980) and Stereophile (1980) but with most mentioning how the large helium tanks may be a major downside. Only a few sold but it definately goes down as one of the best looking tweeters, although the rest of the speaker cabinet was rather more conventional. A reconditioned tweeter unit has been recently demonstrated at AXPONA 2023.

Another notable but rare commercial design that was not based on a Klein RF circuit is the IML DVL Digiplasma, released around 1981. This was a unique PWM (pulse width modulated) design with a nice large open dual glow discharge plasma. It would seem to have had no mitigation for the toxic gas production.

Along with the Magnat mentioned previously the late 70's and early 80's could be seen as the hay-day of plasma tweeter commercial competition.

Part 5 - Don't Breathe

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